Tape samples with up to 1,350 mm length

High precision, low degree formation and clean cut surfaces are the be-all and end-all for applications of metal strips and sheets. Although many measuring systems already allow targeted quality analyses, unfortunately these are only given for short random samples. In the case of large circular knives with wide circumferences, however, defects can go unnoticed - if they do not appear randomly on the sample. In order to ensure greater reliability here and to avoid unusable batches, a more efficient measuring device was developed.

Cutting and straightening machine manufacturer Burghardt + Schmidt, in collaboration with imaging experts FocalSpec, has developed a new, non-contact measuring device for test pieces up to 1,350 mm in length. This measurement corresponds to the full circumference of a circular knife with a diameter of over 400 mm and thus ensures a complete assessment of the entire cutting length. Finally, the system is suitable for materials up to 4 mm thick and records not only the degree and area of cut but also the edge rounding.

Precision at less than 1 µm
The new measuring device belongs to the EP300 series and is based on the same technology as the already proven variant for 250 mm long specimens: In the Lateral Chromatic Imaging (LCI) process, special light spectra are generated and directed onto the cut area. Here they are reflected by the fine structures in the metal, and the specific height differences can be determined on the basis of the dominant wavelengths. The precision with this method is less than 1 µm, the resolution is 2.2 x 20 µm.

A particular advantage is that the tape is not touched during the process, which ensures realistic reproduction without external interference. Also, the sample does not have to be prepared separately for the measurement, so that the quality standard can be checked very easily and early in production

Linear guidance of the measuring head
To ensure uniform movement of the measuring unit over the entire length of up to 1,350 mm, the entire system -including a swivelling mount for PC, monitor, keyboard and mouse- is mounted on a stable aluminium measuring table. The spring-mounted, height-adjustable measuring head is moved by an electric motor using a linear guide. The guide system is mounted on the underside of the table and protected by a cover plate. This prevents blockages or irregularities due to contamination and ensures very high measurement quality.

For optimum conditions, Burghardt + Schmidt also recommends setting up the instrument in a clean room so that no dust from production can be deposited on the sample that would falsify the result.

The system comprises two separate fixtures for strip samples, one of which is designed for the measurement of degree of cut and edge drop and the other for the examination of the cut surface. Calibration of the LCI unit is performed automatically in each case using an integrated reference specimen. The traversing speed of the measuring head is approximately 50 mm/s, which means that a specimen with the maximum length can be completely measured within only 30 seconds. A profile with an optical width of 4 mm is created per millimeter, resulting in a detailed image of the cut edge in its larger environment.

Creation of reports and graphics
Measurement logs, graphics and reports are automatically generated from the information collected in this way and can be saved and replayed directly on the device. The data can also be transferred in CSV or PDF format to an external data storage device for further analysis. The possible graphical display formats range from degree-of-cut profiles at the measuring point or along the entire length, to profiles of the edge indentation and the cut surface, to 3D imaging of the surface around the cut. In this way, the new, larger EP300 measuring device makes it possible to answer all questions relating to cutting quality promptly and, above all, for the complete knife circumference using clear images and clear reports.

Further information on the EP300 series can be found at www.b-s-germany.de.